Businesses and consumers, especially teenagers, frequently desire to display images or messages for a period of time up to months in duration, to be replaced by another image or display. For example, retail stores may periodically display "sale" signs, and teenagers may display posters or pennants of rock stars, athletic heros, or movie stars. The usual means for adhering these images to walls or ceilings are: (1) pins or nails; (2) adhesive tape; or (3) glue, all of which leave more or less damage to the support surface once the image is removed. There is a need for a convenient means to adhere images or messages to support surfaces without damaging the surface.
Moreover, the usual means for binding displays to a wall grip at the periphery, not throughout the entire surface. As a result, after a period of time, displays held by tape or pins will sag or wrinkle. It is desirable to have the display bound to the support surface over the entire back surface of the display.
The principle of electrostatic adhesion is well known. When two dissimilar materials are placed in contact, potential is created between the two materials wherever they actually touch each other. When they are separated, one will have a positive charge and the other will have a negative charge in the area in which they were in contact. A charge may be placed on some materials by rubbing with a static inducing material, such as fur, brushes or fibrous rollers, thus increasing the amount of charge. One material acquires electrons and the other gives them up.
When a charged material is placed close to a wall or other support surface, it creates an equal and opposite charge on the wall under each of the charged areas on the charged material, setting up a mirror image on the wall of the charge that resides in the charged material, but of opposite polarity. Because the two charges are of opposite polarity, they attract each other and the charged material adheres to the wall.
Ordinary paper and plastic sheets may be charged by rubbing with a static inducing material, but the charge bleeds off and the weight of the display material is too great to be retained on a wall or ceiling without a charge-sustaining intermediate material.
The use of electrostatic forces for supporting displays is generally known in the art. Thus, U.S. Pat. No. 3,440,750 shows the adhesion of three dimensional characters to a board by static electricity. Japanese Patent No. 59-111183 discloses a sheet or pocket of a fluoropolymer bonded to an object by rubbing the sheet against the surface to which it is to be bonded.
U.S. Pat. No. 4,652,239 shows a space planning kit in which a horizontal paper substrate is printed with a grid over which vinyl pieces, representing furniture and the like, may be temporarily placed, secured by static electricity.
U.S. Pat. No. 4,741,119 shows a display board with a paper document sandwiched between a charged plastic backing board and a transparent plastic cover of a size larger than the paper document, so that the border of the cover adheres to the backing board along the perimeter.
U.S. Pat. No. 4,225,369 discloses a method of securing a paper sheet backed by or covered with a PVC sheet to a smooth base, including the step of securing the sheet to the base by electrostatically charging the base by rubbing with a rag or the like.
U.S. Pat. No. 4,275,112 discloses the use of an electrostatically chargeable intermediate sheet of doubly charged irradiated and cross-linked insulative plastic foam having a bulk density of about two pounds per cubic foot and a thickness of 1/16 to 1/2 inch. In this document it is taught that the surface of the sheet should be smooth, and that the sheet is to be charged by vigorous rubbing with a hair or wool pad, mounted and recharged.
While these patents generally teach electrostatic adhesion, the problem remains that only relatively light materials can be supported, for example, small photographs, light paper posters and the like. Further, thicker and stiffer foam backings seem to have been used, apparently to provide improved support. This is also disadvantageous, since thinner backings are less obvious in use.
It is thus an object of the present invention to provide an article of manufacture which has improved electrostatic adhesive powers, as well as an improved method for electrostatically adhering objects to a support surface for an extended period of time, which article and method nevertheless use thinner backings than those of the prior art.